The present invention concerns an internal combustion engine having a regulating device.
In the regulating strategy known from EP 0 259 382 B1 a charge pressure reference value is generated in dependence on a measured actual power output of the internal combustion engine and the lambda value (ratio of air to fuel) is so adjusted by a first regulating circuit (charge pressure regulator) by way of a reference value-actual value comparison that the actual charge pressure corresponds to the charge pressure reference value and, at that charge pressure reference value, there is a given target value in respect of the NOx emission. As the NOx emission is not directly known the charge pressure is used as an auxiliary regulating parameter. The function relationship is in the form of a set of curves, wherein each curve for a given NOx value specifies the relationship between actual power output and charge pressure reference value. In that respect therefore the charge pressure regulator is actually an emission control circuit in relation to the NOx emission (NOx emission control circuit).
Adjustment of the lambda value is effected by way of influencing a gas metering device. The change in the lambda value would in itself cause a change in the power output of the internal combustion engine, which must be compensated by a second regulating circuit (output regulating circuit). That compensation effect in the power regulating circuit is implemented by way of those actuators which directly influence the charge pressure (throttle flap and compressor bypass). The charge pressure is therefore regulated indirectly by way of the lambda value. That regulating strategy is known as the LEANOX® method.
Accordingly therefore the functional relationship between the charge pressure which prevails upstream of the inlet valves of the engine and which can be relatively easily measured and the power output is put to use.
For that purpose the output of the charge pressure measuring means is connected to an actual value input of the first regulating circuit. Arranged in the first regulating circuit of EP 0 259 382 B1 (charge pressure regulator) is a programmable device for ascertaining an power output-dependent reference value for the charge pressure, from the power output measurement signal supplied by the power output measuring means.
In that arrangement regulation of the charge pressure is effected indirectly by way of regulation of the combustion air ratio (lambda) in the air-gas mixture, wherein for example leaning of the mixture (increasing lambda) causes an increase in the charge pressure upstream of the inlet valves (in the situation requiring demand for a constant engine power output). It will be noted however that various disadvantages like for example stability problems and a detrimental transient behaviour (slow start required) arise due to coupling of an power output regulation to regulation of the charge pressure (as an alternative to direct NOx emission regulation), while maintaining a target value of NOx emission.
FIG. 1 shows the state of the art in accordance with EP 0 259 382 B1.
The specified logical units do not have to be in the form of physical components but can be embodied in the form of circuits in the regulating device of the internal combustion engine.
FIG. 1 shows the state of the art in accordance with EP 0 259 382 B1. The Figure diagrammatically shows an internal combustion engine 1 to which a combustion gas mass flow ugas is supplied. The combustion gas mass flow ugas can be influenced by way of a regulator 5 which actuates suitable actuators (for example port injection valves or a gas metering device of a gas mixer).
The regulating circuit shown at the top in FIG. 1 is the NOx emission regulating circuit. In this case the NOx emission regulating circuit includes the structural units or logical relationships denoted by references 2, 3, 4, 5 and the respective input and output parameters. It includes in suitable form (for example in the form of a look-up table or a function) the functional relationship 2 between charge pressure reference value pdim (as output of the functional relationship 2) and actual power output Pg (as input of the functional relationship 2) for a given NOx value in the form of a curve. The comparator 3 implements a reference-actual comparison between charge pressure reference value pdim and actual charge pressure pim. The deviation pdim-pim is passed to a PID regulator 4. That outputs a reference value for the lambda value which serves as input for the regulator 5 for actuating the actuators which influence the combustion gas mass flow ugas. The regulator 5 can also be in the form of an open-loop control, that is to say without feedback of the target parameter λd.
The circuit shown at the bottom in FIG. 1 is the power output regulating circuit. It includes a further PID regulator 6 which as input is supplied with the deviation Pdg-Pg, determined in a further comparator 7, between reference power output Pdg and actual power output Pg. The PID regulator 6 produces as output suitable control signals up for influencing the actual charge pressure pim to those actuators (for example compressor bypass valve or throttle flap valve) which influence on the one hand the actual charge pressure pim and on the other hand the actual power output Pg, thereby giving the above-described strong coupling between NOx emission regulating circuit and power output regulating circuit.